Magnetic detent mechanism



July 12, 1966 BEACH, JR, ETAL 3,260,870

MAGNETIC DETENT MECHANISM Filed Dec. 28, 1962 2 Sheets-Sheet 1 22 46 1% ea 2o INVENTORS.

44 65 LAURENCE R. BEACH JR.

A ROBERT J. BLACK July 12, 1966 L. R. BEACH, JR., ETAL 3,260,870

MAGNETIC DETENT MECHANI SM Filed Dec. 28, 1962 2 Sheets-Sheet 2 FIG. 3. '8 A s B 29 ,70 A

31 32 In: 1-I 39 43 I64 68-- I 57 60 .020 2| DETENT 2g ZL g 44 AIR GAP 22 so 5 20 .1 1:111 58 7 FIG. 6. 3""" 1 FIGS.

FIG.8.

ARI 2/ 7' ....nm

' 59 INVENTORS.

LAURENCE R. BEACH JR. ROBERT J. BLACK THEIR ATTORNEYS.

United States Patent 3,260,870 MAGNETIC DETENT MECHANISM Laurence R. Beach, In, San Jose, and Robert J. Black,

Saratoga, Calif., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 28, 1962, Ser. No. 247,947 7 Claims. (Cl. 31014) The present invention relates to detent mechanism, and pertains more particularly to a magnetic detent for a positional member.

In data processing and other mechanisms it is frequently desirable to have a rapidly movable positional member, such as, for example, a transducer support, capable of being accurately positioned at selected points relative to a recording member such as a tape or disk.

In the past, various types of detents have been developed, such as, for example, ratchets and pawls, spring pressed balls, and others. These prior art detents are characterized by frictional engagement between parts thereof, with resultant wear and the requirement for adjustment and servicing.

An object of the present invention is to provide a magnetic detent mechanism wherein a plurality of spaced, magnetic projections are provided on one member which is movable relatively to a second member having a plurality of similarly spaced magnetic projections thereon, so that when the relatively movable members are arrested with their magnetic projections in opposed, slightly spaced relation, the magnetic flux field between the two members draws the projections thereon toward laterally opposite, detenting position.

Another object of the invention is to provide a first plurality of equally spaced apart magnetically permeable elements on a positional member mounted for movement along a path, and to provide a second plurality of similarly spaced apart magnetically permeable elements closely adjacent such path, at least one of the pluralities of magnetically permeable elements being magnetized, so that when the positional member is arrested, portions of the two pluralities of magnetically permeable elements are magnetically drawn into directly opposed, detenting position.

Another object of the invention is to provide an improved, magnetic detent mechanism wherein a shaped, magnetic flux field is the only link between two portions of such mechanism.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings, wherein:

FIG. 1 is a view in isometric projection of a linear actuator embodying the present invention, portions of the base being broken away.

FIG. 2 is a sectional view taken along a plane indicated by the line 22 of FIG. 1.

FIG. 3 is a sectional view taken along line 33 of FIG. 2.

FIG. 4 is an enlarged, fragmentary, side elevational view, looking in the direction of the arrows 44 of FIG. 5.

FIG. 5 is an end view of the magnetic detent members illustrated in FIGS. 1-3.

FIG. 6 is a sectional view taken along line 66 of FIG. 5.

FIG. 7 is a sectional view taken along line 77 of FIG. 5.

FIG. 8 is an enlarged, fragmentary view, somewhat 3,260,870 Patented July 12, 1966 similar to FIG. 4, but showing a modified form of magnetic detent member.

FIG. 9 is a view in isometric projection of a tachometer embodied in the mechanism shown in FIGS. 1 and 2, portions being broken away.

Briefly, the form A of the invention shown in FIGS. l-3 comprises a magnetically permeable, toothed, racklike detent member 10, which may be of mild steel, secured lengthwise along a side of a positional member 11. The latter in turn is supported by low friction bearings 12 and 13 for linear, slidable movement along a fixed track rod 14.

A straight line drive motor B, which type is desirable due to its rapid rate of acceleration, comprises a coil 15 secured to an end of the positional member 11 and coaxially of the track rod 14. The motor coil 15 is mounted for axial driving movement within the working air gap 17 (FIG. 2) of an annular field magnet assembly 18, which in turn is mounted on a supporting base plate 19.

A horseshoe type permanent magnet 20', having endwise directed teeth 21 on the end of each leg thereof, is mounted on a standard 22 secured to the base plate 19 by screws 22a. The magnet teeth 21 have the same pitch as those 23 of the detent member 10, and are directed toward, are parallel to, and are spaced slightly from, the path of movement of the teeth 23 on the detent member 10. The magnetic flux field between the teeth 22 of the horse shoe magnet 20 and those 23 of the detent member 10 tends to draw the two opposite sets of teeth thereon to their closest possible position, which is directly opposite each other as shown in FIG. 4.

Referring to the drawings in greater detail, in the illustrative mechanism A (FIGS. 1-3) the positional member 11 is of non-magnetically permeable material, such as, for example, aluminum. It is a generally rectangular, elongated block, with a hole 24 longitudinally therethrough, and a pair of rabbeted grooves 27 and 28 in the upper and lower corners, respectively, of one side thereof to provide tracks for guide rollers 29 and 30. These rollers may be small, conventional ball bearings, and are journaled on posts secured to the magnet support standard 22. A gap 31 (FIG. 1) is provided at one side of a magnet receiving opening 32 in the magnet support standard 22, and a screw 33, inserted in a hole provided therefor above the gap 31, and screwed to adjusted position into a threaded continuation of this hole below the gap, may be used to adjust the rollers 29 and 30 into close, freerolling, guiding relation with their respective track surfaces on the positional member 11.

The low-friction support bearings 12 and 13 for the positioned member 11 are mounted co-axially in the hole 24 to provide free bearing support for the positional member and its associated part-s upon the track rod 14. These bearings 12 and 13 may be of the well known, longitudinally circulating ball bearing type, although the specific type of low friction bearing used is not material to the invention. These bearings are inserted with a light press fit into opposite ends of the hole 24, and seat on shoulders provided by offsets between larger diameter end portions 24a and 24b of the hole 24 and a smaller diameter medial portion 240.

A coil support member 37 of non-magnetic material, such as aluminum, is mounted on an end of the positional member 11 for movement co-axially of the track rod 14. The coil support member 37 comprises a hub portion 38, inserted with a light press fit co-axially into the hole 24 in the positional member 11, and a co-axial rim portion 39 which bears against the end of the positional member 11. The motor coil 15 is mounted co-axially on the rim 39, and is c-oreless for lightweight and to provide a substantial length of coil conductor in the working air gap 17 of the linear motor B of which it forms a part.

A preferred form of motor coil is made by winding usual magnet wire of a desired size upon a removable cylindrical mandrel (not shown) which may be of soluble or low melting point material, and having an external diameter equal to the desired inside diameter of the coil. Before winding the coil 15, the wire is first coated with catalyzed, unset, epoxy resin. After the coil has been wound, it is set aside until the epoxy has set, after which the core is removed, as by immersing it and the coil wound thereon in a solvent for the core materials, or by heating it above the melting point of the core material. Epoxy resin also may be employed to adhere the coil 15 co-axially to the rim 39 of its support 37.

Flexible conductor leads 40 (FIG. 2) from the coil 15 may be used to connect the latter into a suitable circuit (not shown) for actuating the linear motor B to drive the positional member 11 to a desired address lengthwise thereof. Since such circuits are well known to those familiar with the design and operation of data processing mechanisms with which the present invention is intended to be used, and since the particular circuit employed is not material to the invention, it is omitted to avoid unnecessary complication of the present disclosure.

The field magnet assembly 18 of the motor B comprises a pair of ring magnets 41 and 42, which are of suitable permanent magnet material, and are powerfully magnetized in a well known manner. An annular end member 43, which may be of mild steel, is secured, by screws 44a, in axially horizontal position, to a motor support standard 44 of preferably non-magnetic material such as aluminum. The latter is secured by screws 45 to the base plate 19. The annular end member 43 is provided with a peripheral flange portion 43a (FIG. 2) which fits over the end of the ring magnet 42, and a thicker central portion 43b which fits snugly, co-axially therein.

The central opening 47 in the annular end member 43 is of slightly larger diameter than the motor coil 15, so as to have a working clearance therefrom when the coil is mounted for movement co-axially therein, as best shown in FIG. 2.

A disk end member 48 of magnetically permeable material, such as mild steel, is provided on the opposite end of the other ring magnet 41 from the annular end member 43, and is generally similar thereto with the exception that it has no central opening. The magnet assembly 18 is secured co-axially together by screws 49, inserted through holes provided therefor in the end members 43 and 48, and screwed into threaded holes provided therefor in a sleeve 46 (FIG. 2) of non-magnetic material, such as aluminum, inserted co-axially within the ring magnets 41 and 42.

A cylindrical core block 50, which may be of mild steel, is fitted into a central recess provided therefor in the end disk 48, and is secured therein, co-axially of the annular magnets 41 and 42 by a screw 51. The core block 50 is of a length to extend into the central opening 47 of the annular end member 43, and terminates substantially flush with the outer face of the end member. The core block 50 is of slightly smaller diameter than the coil 15, so as to have a working clearance therefrom when mounted co-axially therein as shown in FIG, 2.

One end of the track rod 14 is fitted into a hole provided therefor co-axially of the core block 50, while its other end is supported in a bracket 52 of non-magnetic material, such as aluminum, secured to the base plate 19 by screws 53.

A damping tachometer C (FIGS. 1-3 and 9), which preferably is employed to prevent overrunning of the positional member 11, comprises a pair of similar coils 54 and 55, with their windings connected in series, and transversed by a horseshoe magnet 57 secured to the under side of the positional member 11 for movement therewith. The tachometer coils 54 and 55 are wound on parallel core rods 58 and 59, respectively, which may be of mild steel. The core rods 58 and 59 are magnetically coupled at one end thereof by being fitted into holes provided therefor in a magnetically permeable block 60, which in turn is fastened by screws 61 to the motor support standard 44. The opposite ends of the core rods 58 and 59 are fitted into holes provided therefor in the track rod support bracket 52 with the core rods parallel to the track rod 14.

The tachometer horseshoe magnet 57 may be of suitable magnet material, properly magnetized, and is secured by a screw 62 (FIG. 3) to the under side of the positional member 11, with the lower ends of its legs centered over the tachometer coils and spaced slightly therefrom. Thus, when the tachometer magnet 57 is carried along these coils 54 and 55 by a movement of the positional member 11, voltage will be generated in the coils in accordance with the principle that voltage is generated by a conductor moving through a magnetic field, and is proportional to its speed. This principle is expressed by the formula: E=6.5 10" Blv, where E the voltage in volts, B=fiux density in gauss, l=length of conductor in inches, v=velocity of conductor in inches per second.

The magnetic detent member 10 may be of mild steel, fiat bar stock, with the teeth 23 milled therein. The racklike member thus formed is fitted into a groove provided therefor lengthwise of the positional member 11 parallel to the axis of the hole 24, and is secured therein by screws 63. The parallel, equally spaced teeth 23 extend transversely across the detent member 10, and may be of the profile indicated in FIG. 4.

The illustrated detent magnet 20 is a powerful, permanent, horseshoe magnet of suitable material, and the endwise extending teeth 21 provided on the ends of its legs are of the same pitch, or center-to-center spacing, as those 23 of the detent member 10. The teeth on each leg of the detent magnet 20 are aligned with those on the other leg, as best illustrated in FIG. 7.

The detent magnet 20 is supported on its standard 22 with its teeth 21 spaced from those 23 of the detent member 10 by being mounted on a bar 64, preferably of nonmagnetic material such as aluminum, of a size and shape to fit snugly into the re-entrant space between its legs.

The magnet 20 is mounted in the opening 32 provided therefor in the standard 22, which also is of non-magnetic material, such as aluminum, the magnet hole 32 therein being of a size and shape to admit the magnet 20 freely therein.

A pair of magnet supporting and adjusting screws 65 are screwed into threaded holes provided therefor, one at each end of the magnet support bar 64. Each screw 65 has an unthreaded axial extension 67 (FIG. 2) of slightly reduced diameter on its inner end, which extension fits snugly, but rotatably, into a hole provided therefor in the magnet standard 22. These axial extensions 67 support the magnet 20 with the outer ends of its teeth parallel to the teeth of the detent member 10.

The magnetic attraction of the detent magnet 20 for the magnetically permeable detent member 10 opposite thereto urges the magnet 20 toward the detent member 10, while the shoulders between the threaded shanks of the screws 65 and their reduced extensions 67, hearing against the standard 22, limit the extent to which the detent magnet 20 may thus be drawn. Turning the screws 65 in the threaded hole in which they are mounted in the magnet support bar 64 in a required direction thus controls the clearance between the teeth 21 on the magnet 20 from those 23 on the detent member 10. This clearance should be small, preferably of the order of a few thousandths of an inch or less for maximum magnetic attraction, but should be adequate to insure against physical engagement of the teeth of the magnet 20 and the detent member 10. Lock nuts 68 anchor the screws 65 in adjusted position.

The base portion 69 of a conventional transducer support arm is shown secured to the upper side of the positional member 11 by screws 70. This support arm 69 may carry on its outer end portion, which is broken away, a conventional transducer (not shown) for operative association with, for example, selected tracks of a magnetic coated recording disc or tape spaced on centers equal to the pitch of the detent teeth 21 and 23. With the tooth structure shown in FIG. 4 this spacing would be .020 inch.

The operation of the illustrated form of the invention is as follows: The straight line motor 'B, by means of an electrical current applied to its coil 15 by conventional circuitry, not shown, drives the positional member 11 inwardly or outwardly as required, and arrests it in a position within a few thousandths of an inch of its final address. Accuracy in arresting the positional member adjacent its required address is assisted by the tachometer C, which, as the velocity of the positional member 11 increases, generates a voltage which is employed to create a damping effect on the action of the motor B.

This damping effect provided by the tachometer C assists in preventing overrunning at the end of a movement of the positional member 11. The accuracy of such arrested position must be within less than one-half the pitch of the teeth of the detent members and 20in order that the substantial magnetic detent action will draw the parts to their required final position. In such arrested position of the positional member 11, upon de-energization of the motor coil 15, the magnetic flux field of the detent magnet 20 will be shaped by the teeth 21 of the magnet 20 to attract the teeth 23 of the detent member 10 most nearly opposite thereto, and will thereby magnetically draw each of the teeth 23 toward its closest relative position to the tooth 21 nearest thereto, thereby tending to position each tooth 23 directly opposite a tooth 21 as shown in FIG. 4.

The support bearings 12 and 13 for the positional member 11 must have a sufliciently low coeificient of friction on the track rod 14 to permit this final detenting action, but since each pair of opposed teeth of the two detent members 10 and 20 act as a separate pair of magnets tending to move into directly opposed relation, a very substantial detenting force is thus exercised to position and retain the positional member 11 in its required, final address position. Employing a tooth pattern such as that shown in FIG. 4, a mechanism such as that shown in FIGS. 1-3 has consistently achieved .020 inch steps (pitch of both sets of detent teeth) in times of ten milliseconds, With a detent accuracy of plus or minus .0002 inch.

While the detent magnet 20 is illustrated as a permanent magnet, and the detent member 10 as a rack-like member of magnetically permeable material, either or both of these members may be electro-magnets, and in such case may be energized only at the moment of final detent positioning. Also, either or both of these members may comprise aligned pluralities of magnetic elements 71 (FIG. 8), spaced apart by non-magnetic spacers 72. These magnetic elements may be either permanently magnetized, or electro-magnetically magnetized as desired.

The invention provides a simple, accurate, friction-free, magnetic detent mechanism, wherein the detenting force is created by the unique shaping of a flux field, and the magnetic flux is the only link between the detent members. The invention may be readily embodied in a large number of mechanisms requiring accurate positioning of a p0sitional member. Once installed and adjusted, detent mechanisms embodying the invention will operate indefinitely without wear or the requirement of servicing, in the absence of mishandling or externally applied damaging forces.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. A magnetic detent mechanism comprising;

(a) a positional member mounted for free movement along a path,

(b) drive means for driving the positional member to each of a plurality of selected positions along such path,

(c) dent mechanism for accurately centering the positional member in each of such selected positions, said detent mechanism comprising a first plurality of simultaneously magnetized magnetic elements mounted on the positional member in equally spaced, aligned relation along and parallel to such path, and

(d) a second plurality of magnetic elements fixedly mounted in the same spaced, aligned relation closely adjacent and parallel to such path, and spaced slightly from the first plurality of magnetic elements, and so positioned that in each of such selected posi tions of the positional member a plurality of the teeth of both pluralities thereof are in directly opposite relation to each other to magnetically center and retain the positional member in such position.

2. A magnetic detent mechanism as claimed in claim 1 wherein one of the plurality of magnetic elements extends substantially the entire length of such path.

3. A magnetic detent mechanism comprising;

(a) a positional member mounted for free movement along a path,

(b) drive means for driving the positional member to each of a plurality of selected positions along such path,

(c) detent mechanism for accurately centering the positional member in each of such selected positions, said detent mechanism comprising a rack-like member mounted on the positional member,

(d) a plurality of magnetically permeable teeth on the rack-like member, said teeth being spaced apart and aligned along a line parallel to the path of movement of the positional member,

(e) a magnet mounted adjacent such path,

(f) a plurality of magnetically permeable, aligned teeth on a magnetized pole portion of the magnet, said teeth on the magnet being spaced the same as the teeth of the hack-like member (g) the magnet being mounted with its teeth facing, parallel to, and spaced slightly from, those of the rack-like member, and so positioned that in each of such selected positions of the positional member the teeth of the magnet are in directly opposite relation to an equal number of teeth of the rack-like member to magnetically center and retain the positional member in such position.

4. A magnetic detent mechanism comprising;

(a) a track,

(b) a positional member mounted on low friction bearings on the track for free, guided movement therealong,

(c) drive means for driving the positional member to each of a plurality of selected positions along the track,

(d) detent mechanism for accurately centering the positional member in each of such selected positions, said detent mechanism comprising a first plurality of magnetically permeable elements mounted in equally spaced relation on the positional member and aligned parallel to the path of movement of the positional member along the track, and

(e) a second plurality of magnetically permeable elements aligned and spaced the same as the first plurality of magnetically permeable elements,

(f) means for simultaneously magnetizing the magnetically permeable elements of one plurality thereof,

(g) the second plurality of magnetically permeable elements being fixedly mounted parallel to, facing, and spaced slightly from the first plurality of magnetically permeable elements, and being so positioned that in each of such selected positions of the positional member a plurality of the magnetically permeable elements of both pluralities thereof are in directly opposite relation to each other to magnetically center and retain the positional member in such position.

5. A magnetic detent mechanism as claimed in claim 4 wherein means are provided for adjusting the second plurality of magnetically permeable elements toward and away from the first plurality of magnetically permeable elements.

6. A magnetic detent mechanism comprising a positional member mounted on low friction bearings for movement along a path, means for driving the positional member to each of a plurality of selected positions along such path, and a fixed member mounted adjacent said path, said detent mechanism comprising;

(a) a first plurality of magnetic elements mounted in spaced relation on the positional member for movement therewith (b) ends of the first plurality of magnetic elements being aligned parallel to the path of movement of the positional member.

(c) a second plurality of magnetic elements mounted on the fixed member in spaced relation the same as that of the first plurality of magnetic elements, the magnetic elements of one plurality thereof being magnetized,

(d) the second plurality of magnetic elements being mounted with ends thereof aligned similarly to those of the first plurality of magnetic elements,

(e) the aligned ends of both pluralities of magnetic elements being directed toward, parallel to, and spaced slightly from each other, and so positioned that in each of such selected positions of the positional member a plurality of the magnetic elements of both pluralities thereof are in directly opposite relation to each other to magnetically center and retain the positional member in such position.

7. A magnetic detent mechanism comprising;

(a) a positional member mounted for free movement along a path,

(b) a permanent magnet mounted on the positional member with a pole thereof exposed,

(c) an elongated tachometer coil fixedly mounted with its axis parallel to the path of movement of the positional member and spaced slightly from the exposed pole of the magnet,

((1) drive means for driving the positional member to each of a plurality of selected positions as determined by the tachometer coil along such path,

(e) a first plurality of spaced, magnetically permeable elements on the positional member with ends thereof aligned along a line parallel to the path of movement of the positional member,

(f) a second plurality of similarly aligned magnetically permeable elements spaced the same as, and fixedly mounted adjacent the first plurality of magnetically permeable elements and with aligned ends of the second plurality of magnetically permeable elements directed toward, parallel to, and spaced slightly from the aligned ends of the first plurality of magnetically permeable elements, and so positioned that in each of such selected positions of the positional member a plurality of the magnetically permeable elements of both pluralities thereof are in directly opposite relation to each other, and

(g) means for magnetizing the magnetically permeable elements of one plurality thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,627,040 1/1953 Hansen 310-49 2,677,090 4/1954 Fleming-Williams et al.

310-49 X 3,004,111 10/1961 Hollingsworth l79--100 3,162,796 12/1964 Schreiber et al. 310-12 X FOREIGN PATENTS 775,101 5/1957 Great Britain.

OTHER REFERENCES Mukai: Random Accessing of Flexible Magnetic Sleeve, IBM Technical Disclosure Bulletin, vol. 2, No. 5, February 1960, page 35.

LARAMIE E. ASKIN, Primary Examiner.

JOHN P. WILDMAN, JOHN F. BURNS,

Assistant Examiners. 

1. A MAGNETIC DETEND MECHANISM COMPRISING; (A) A POSITIONAL MEMBER MOUNTED FOR FREE MOVEMENT ALONG A PATH, (B) DRIVE MEANS FOR DRIVING THE POSITIONAL MEMBER TO EACH OF A PLURALITY OF SELECTED POSITIONS ALONG SUCH PATH, (C) DENT MECHANISM FOR ACCURATELY CENTERING THE POSITIONAL MEMBER IN EACH OF SUCH SELECTED POSITIONS, SAID DETENT MECHANISM COMPRISING A FIRST PLURALITY OF SIMULTANEOUSLY MAGNETIZED MAGNETIC ELEMENTS MOUNTED ON THE POSITIONAL MEMBER IN EQUALLY SPACED, ALIGNED RELATION ALONG AND PARALLEL TO SUCH PATH, AND (D) A SECOND PLURALITY OF MAGNETIC ELEMENTS FIXEDLY MOUNTED IN THE SAME SPACED, ALIGNED RELATION CLOSELY ADJACENT AND PARALLEL TO SUCH PATH, AND SPACED SLIGHTLY FROM THE FIRST PLURALITY OF MAGNETIC ELEMENTS, AND SO POSITIONED THAT IN EACH OF SUCH SELECTED POSITIONS OF THE POSITIONAL MEMBER A PLURALITY OF THE TEETH OF BOTH PLURALITIES THEREOF ARE IN DIRECTLY OPPOSITE RELATION TO EACH OTHER TO MAGNETICALLY CENTER AND RETAIN THE POSITIONAL MEMBER IN SUCH POSITION. 